Flexible packaging laminates have been used for many years for packaging food products. For example, milk has been packaged in cartons made from a laminate of paperboard with a coating of polyethylene on both sides so that the surfaces of the carton can be heat-sealed together to form a carton of the desired shape. Some food products, such as orange juice, lose their nutritional value due to the penetration of oxygen through the wall of the carton. To reduce the penetration of oxygen into the carton and to minimize the degradation of nutrients such as vitamin C and to minimize the absorption of the flavor oils into the packaging laminate, it has been common to add a layer of aluminum foil to the laminate. Although aluminum foil is effective as a barrier material, its use raises environmental concerns. Various attempts have been made to develop practical alternatives to aluminum foil that have superior oxygen, gas and aroma barrier properties, and yet are readily disposable after use.
In the process of packaging food products, a carton blank may be folded along one or more crease lines to allow the carton to be properly shaped and to form overlapping portions of the packaging material to form a seal either by the application of a suitable adhesive, or by heat-sealing thermoplastic layers together. Creasing of the laminate imposes stresses on the laminate which may be sufficiently great to cause leakage, or may at least weaken the laminate sufficiently so that subsequent handling of the carton may lead to leakage.